Method of manufacturing arsenate of lead.



I ZbaZZ whom it may concern:

UNITED STATES PATENT OFFICE.

EDWIN '0. BMW, OF MIDLAND, MICHIGAN, ASSIGNOR. TO THE DOW CHEM ICAL COMPANY, OF .MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

METHOD OF EANUFAGTUZRING ARSENATE'OF LEAD.

in Drawing.

Specification cit Letters ratent.

Application filed June 10, 1911. Serial .Io. 632,444.

Patented J une 16, 1914.

Be it known that I, EDWIN a citizen of the United States, and a resident of Midland, county of Midland, and State of Michigan, have invented a new and useful Improvement in Methods of Manufacturing Arsenate of Lead, of' which the following is a specification, the principle of the invention being herein explained and the best mode in which I have contemplated applying thatprinciple, so as to distinguish namely lead arsenate and sodium chlorid. The present method, or process, may be;

regarded as a modification or specific aspect of the general process of. manufacturing it from other inventions.

lead arsenate presented in my co-pending application filed June 10, 1911, Serial No. j In this case, as in such eneral process, the mode ofproo'edure invo ved is 1 equally applicable to the manufacture of;

other insoluble metallic arsenates than such lead arsenate, as for example, zinc, iron, and lprocess constituting consists of the steps hereinafter fully described and pan;

barium arsen'ates. The

the present invention, t en,

ticularly pointedout in the claims.

in which theprineiple of the invention may be used.

step consists in adding hydrochloric acid to lead arsenate is being made. The result of such treatment of the sodium arsenate solution with hydrochloric acid is the formation of a complex solution containing sodium arsenate, free arsenic acid, sodium chlorid, and free hydrochloric acid. The following reaction expresses this result, so far as the formation of the arsenic acid and sodium 0. BA-ns'row,

chlorid is concerned Na,HAsQ +2HCl=H AsO +2NaCL The-remaining step, referring for the sake of illustration to the case where it is lead arsenate that is wanted, is carried out by adding to the solution resulting from the aforesaid reaction, an oxid, hydrate, carbonate, or basic carbonate of lead, which re sults in the formation of the end products,

Either or both of the following reactions may be used to explain the production of the compounds just named:

The foregoing operations, involving the addition of the hydrochloric acid to the arsena't'e and of the lead oxid, or equivalent oxygen derivative of lead, to the resulting solution are satisfactorily conducted in. a The followin description sets forth {.in 1.

detail an approved mode of carrying out the invention, such disclosed mode,-.-however, being merely illustrative of the various ways wooden tank provided with a suitable stirrer. Furthermore the second of said operations is conducted with the solution so concentrated that the resulting mass will have the consistency of a cream or paste. It

I has been discovered that, by sufiiciently pro- In the present improved method or pro'c- 2 ess of obtaining lead animate, the initialfact that at first it would seem that this reaction could not be carried to completion because the resulting product, being solid, all of the lead oxid would not be reacted upon but particles of it would be inclosed in an impervious coating of the lead arsenate. By subjecting the liquid, however,'to prolonged stirring or agitation this tendency has been successfully overcome, as above indicated. The lead arsenate so obtained may be conveniently separated out by filtration, and should be washed to remove the soluble salts that are mixed with it.

In the preceding description the addition of the hydrochloric acid lead oxid have been referred to as separate operations, the mud ,pf fact, they'may' be added simultaneously,

being added first, then the oxid; as a matter or .the order reversed, if for any reason found desirable. Preferably the amount of hydrochloric acid used should be slightly less than an equivalent to the base present in the sodium arsenate used;' and the amount of lead oxid used should be sli htly less than that required to react with afi the free acid present. In case these compounds are used in the relative quantities just indicated, there will be left in the final filtrate some soluble arsenic, thatis either arsenic acid or soluble arsenate. These may be recovered in any suitable fashion before discarding the filtrate.

'The oxygen derivatives of lead, which are suitable for use as compounds of that metal for reacting with arsenic acid to form lead arsenate, have been already indicated. The

' term oxygen derivative is intended there- -oxid, in addition tothose which have been fore to connote such equivalents of lead specifically named, as will form the arsenate under the conditions surrounding the reaction. B way of general comment it should further be noted that the acid lead arsenate" PbHAsQ and normal arsenate Pb (AsO,) ar both commonly known to the trade as arsenate of lead. The latter term is accordngly to be understood as used herein in th1s general sense, and not as referring specifically to either of the two arsenates named, except where the contrary is indicated. So too, a soluble alkaline earth arsenate may be used instead of the alkaline arsenate hereinbefore specified as the preferred soluble arsenate, as will be readily understood, and such equivalent is intended to be connoted by the term f alkaline as herein employed. Similarly hydrochloric acid, it will be understood, is typical of any acid that, combined with the metal of which the arsenate i desired, forms a compound more soluble than such arsenate. Thus acetic acid in the case of the manufacture of lead arsenate may be used in place of the hydrochloric acid with satisfactory results.

It is proper to state by way of conclusion that the several equations which have been hereinbefore referred to as expressive of the different reactions involved, have been re sented as illustrative merely of the princlpal ph nomtna. They do not, however, necesj sa'rily represent all of the reactions that ocour, and should be understood to indicate "whole series of detailed reactions pertaining to each particularstep or sub-process described above, as a sin le comprehensive reaction, in whlch only t e starting materials and observed end-products are given. Thus for example, the specific mode of operation herein claimed may be represented as follows Other modes of applying the principle of my invention may be em loyed instead of the one explained, change being made as regardsthe process herein disclosed, provided the step or steps stated by any one of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctlycclaim as my invention 1. The method of makin a relatively insoluble metal arsenate, W ich consists in treating a soluble arsenate other than arsenic acid with an acid that, combined with said metal, forms a compound more soluble than the. arsenate of said metal; and mixing. the resulting solution with a suitable com-" pound of said metal, whereby such relatively less soluble arsenate is formed.

' 2. The method of makin .a relatively insoluble metal arsenate, w ich consists in treating an alkaline arsenate with a halogen acid; and mixing the resulting solution with a suitable comfpound of said metal, whereby the arsenate 0 said metal is formed.

3. The method of makin a relatively insoluble metal arsenate, w ich consists in treatingan alkaline arsenate with a halo en acid; and mixin the resulting solution with an oxygen erivative of said metal,

whereby the arsenate of said metal is formed.

than lead arsenate; and mixing the resulting solution with a suitable compound of lead, whereby such relatively less soluble arsenate'is formed.

6. The method of making lead arsenate, which consists in treatin an alkaline arsenate with a halogen aci and mixing the resulting solution with a suitable compound of lead, whereby lead arsenate is formed.

7. The method of making lead arsenate, which consists in treatin an alkaline arsenate with a halogen aci and mixing the resulting solution with an oxygen derivative of lead.

8. The method of making lead arsenate, which consists in treating sodium arsenate with hydrochloric acid; and mixing the resulting solution with lead oxid.

9. The method of making lead arsen'ate, which consists in treating sodium arsenate with hydrochloric .acid in amount not more than equivalent to the base of said arsenate; and mixing the resulting solution with lead oxid.

10. In a method of making the arsenate of a metal, the step which consists in treating a soluble salt of arsenic acid with an acid that, combined with said metal, forms a compound more soluble than its arsenate.

11. In a method of making the arsenate of a metal, the step which consists in treating sodium arsenatewith, hydrochloric acid not more than equivalent to the base in said arsenate' 12. In a method of making lead arsenate, the step which consists in treating a soluble salt of arsenic acid with an acid, that comequiva bined with lead, forms a compound more soluble than lead arsenate.

13. The methodof making lead arsenate, which consists in treating sodium arsenate with h drochloric acid in amount less than l ent to the base in said arsenate; and mlxing the resulting solution with lead oxid.

14. The method of making lead arsenate which consists in treating sodium arsenate with hydrochloric acid in amount less than equivalent to the base in said arsenate; and mixing the resulting solution with lead oxid, such oxid being insuflicient in amount to combine with all the free acid present;

Signed by me this 6th day of June, 1911.

, EDWIN O. BARSTOW.

Attested by- G. LEE CAMP, D. A. NEWLAND.. 

